This invention relates in general to insulation products made from fibrous minerals like glass and, in particular, to quality control methods for determining the cure status, i.e. whether the product is undercured, overcured or properly cured within specifications and process control limits.
Fibrous glass insulation products generally comprise randomly-oriented glass fibers bonded together by a cured thermosetting polymeric material. Molten streams of glass are drawn into fibers of random lengths and blown into a forming chamber or hood where they are randomly deposited as a pack onto a porous, moving conveyor or chain. The fibers, while in transit in the forming chamber and while still hot from the drawing operation, are sprayed with an aqueous dispersion or solution of binder. The residual heat from the glass fibers and combustion gases, along with air flow during the forming operation, are sufficient to vaporize and remove much of the sprayed water, thereby concentrating the binder dispersion and depositing binder on the fibers as a viscous liquid with high solids content. Ventilating blowers create negative pressure below the conveyor and draw air, as well as any particulate matter not bound in the pack, through the conveyor and eventually exhaust it to the atmosphere. The uncured fibrous pack is transferred to a drying and curing oven where a gas, heated air for example, is blown through the pack to dry the pack and cure the binder to rigidly bond the glass fibers together in a random, three-dimensional structure, usually referred to as a “blanket.” Sufficient binder is applied and cured so that the fibrous pack can be compressed for packaging, storage and shipping, yet regains its thickness—a process known as “loft recovery”—when compression is removed.
While manufacturers strive for rigid process controls, the degree of binder cure throughout the pack may not always be uniform for a variety of reasons. Irregularities in the moisture of the uncured pack, non-uniform cross-machine weight distribution of glass, irregularities in the flow or convection of drying gasses in the curing oven, uneven thermal conductance from adjacent equipment like the conveyor, and non-uniform applications of binder, among other reasons, may all contribute to areas of over- or under-cured binder. Thus it is desirable to test for these areas in final product to assure quality.
U.S. Pat. No. 4,363,968 to McGowan, et al.; U.S. Pat. No. 4,582,520 to Sturm; and U.S. Pat. No. 4,609,628 to Aschenbeck, all teach methods of using multiple wavelengths of infrared (“IR”) radiation to monitor the amount of binder or the degree of cure of the binder in a fiberglass mat product. In general, they all rely on differences in the IR absorption/transmission between the binder chemical reactants (carboxylic acid groups and alcoholic groups) and the cured binder products (ester groups). U.S. Pat. No. 4,769,544 to Dahlquist, and U.S. Pat. No. 7,435,600 to Packard are similar, except they rely on different wavelengths of IR and/or different ratios of reactants/products.
U.S. Pat. No. 7,520,188 discloses a destructive, off-line method of dying and scanning a fiberglass product, and performing a color analysis of red pixel ratio to determine a degree of cure.
While each of these methods had advantages, there are also drawbacks. The IR methodologies to date rely on transmission of radiation through the fibrous pack in one direction and thus are not capable of providing information about cure at various depths of the pack.